Nucleotides, Nucleic Acids and Heredity

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Nucleotides, Nucleic Acids and Heredity

• Bettelheim, Brown, Campbell and Farrell
• Chapter 25

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Nucleic Acids--Intro

• Chromosomes contain genetic information
• found primarily in nucleus
• Chromatin tightly packed DNA and histones
• Chromosomes contain DNA and basic proteins
  (histones)
• Can be seen during cell division
• Nucleic acids are responsible for genetic
  information

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Introduction

• Cells contain thousands of different proteins
• How do cells know which proteins to synthesize?
• First thought that transmission of hereditary
  information took place in the nucleus (in
  chromosomes) beginning late in 19th century
• Hereditary information thought to be in genes
  within the chromosomes
• Chemical analysis of nuclei showed chromosomes
  are made up largely of proteins called histones
  and nucleic acids

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Introduction

• By the 1940s it became clear that
  deoxyribonucleic acids (DNA) carry the hereditary
  information
• Other work in the 1940s demonstrated that each
  gene controls the manufacture of one protein
• Thus, the expression of a gene in terms of an
  enzyme protein led to the study of protein
  synthesis and its control

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Categories of Nucleic Acids

• Deoxyribonucleic Acid (DNA)
• Found in nucleus (in chromosomes)
• Contain genes which contain genetic
  information
• Ribonucleic Acid (RNA)
• Some found in nucleus (but not in chromosomes)
• Also found in cytoplasm

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• Both DNA and RNA contain
• A Nitrogenous Base
• Sugar
• Phosphate
• Nucleoside contains just a base and a sugar
• Nucleotide contains all three components

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Nucleic Acid Bases
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Purine BasesAdenine Guanine
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Pyrimidine BasesCytosine Thymine Uracil
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Pyrimidine/Purine Bases
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DNA and RNA Bases

• DNA RNA
• Adenine Adenine
• Thymine Uracil
• Guanine Guanine
• Cytosine Cytosine

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Sugar
Ribose
2-Deoxyribose
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• Both DNA and RNA contain
• A Nitrogenous Base
• Sugar
• Phosphate
• Nucleoside contains just a base and a sugar
• Nucleotide contains all three components

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Nucleoside
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Nucleosides

• Nucleoside a compound that consists of D-ribose
  or 2-deoxy-D-ribose bonded to a purine or
  pyrimidine base by a ?-N-glycosidic bond

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Nucleotide
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Nucleotides

• Nucleotide a nucleoside in which a molecule of
  phosphoric acid is esterified with an -OH of the
  monosaccharide, most commonly either the 3 or
  the 5-OH

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Nucleotides

• adenosine 5-triphosphate (ATP) serves as a
  common currency into which energy gained from
  food is converted and stored

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Structure of DNA and RNA

• Primary Structure the sequence of bases along
  the pentose-phosphodiester backbone of a DNA or
  RNA molecule
• base sequence is read from the 5 end to the 3
  end

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Nucleic Acid - 1 Structure

• A schematic diagram of a nucleic acid

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Fig. 24.3
3 end of one sugar to phosphate to 5 end of
second sugar
3,5 phospho-diester linkage
Each nonterminal phosphate has -1 charge
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Pyrimidine BasesCytosine Thymine Uracil
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Fig. 24.3, p.602
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Structure of DNA and RNA

• Primary Structure the sequence of bases along
  the pentose-phosphodiester backbone of a DNA or
  RNA molecule
• base sequence is read from the 5 end to the 3
  end

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Nucleic Acid Structure

• DNA has a double helix structure
• Phosphates on outside
• Complementary Base Pairs on inside
• RNA is single stranded
• Messenger RNA (m-RNA)
• Transfer RNA (t-RNA) has some double stranded
  loops

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DNA - 2 Structure

• Secondary structure the ordered arrangement of
  nucleic acid strands
• Double helix model of DNA 2 structure was
  proposed by James Watson and Francis Crick in
  1953
• Based on two primary sources of information
• Irwin Chargaff A T and C G
• X-ray diffraction picture of DNA taken by
  Rosalind Franklin

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Irwin Chargaff Base Composition in Many
Different Species
Table 24.2, p.602
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Rosalind Franklin
p. 640
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James Watson Francis Crick
p. 640
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• Double helix
• a type of 2 structure of DNA molecules in which
  two anti-parallel polynucleotide strands are
  coiled in a right-handed manner about the same
  axis

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DNA Double Helix

• Double helix
• Two DNA strands
• Anti-parallel strands
• One is 3 to 5 Other is 5 to 3
• Strands are coiled in a right-handed helix about
  the same axis
• Backbone has alternating sugar and phosphate
  groups
• Complementary Base Pairs on inside of helix

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The DNA Double Helix
Each turn is 3.4 nm
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Complementary Base Pairs

• DNA Base Pairs Double-Stranded
• A-T A T
• C-G C G
• RNA Base Pairs Single-Stranded
• A-U
• C-G

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Complementary Base Pairs

• Must be one purine and one pyrimidine to fit
  properly
• Two purines too big
• Two pyrimidines too small
• Not every purine-pyrimidine pair forms naturally

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Fig. 24.6, p.605
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Complementary Base Pairs
2 H-bonds
TA pair
GC pair
3 H-bonds
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Non-Complementary Base Pairs
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Chains are anti-parallel
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Fig. 24.5
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Fig. 24.4
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Higher Structure of DNA

• DNA is coiled around proteins called histones
• Histones are rich in the basic amine acids Lys
  and Arg, whose side chains have a positive charge
• DNA molecules (with charge) and histones (with
  charge) attract each other and form units
  called nucleosomes
• nucleosome a core of eight histone molecules
  around which the DNA helix is wrapped
• nucleosomes are condensed into chromatin
• chromatin fibers are organized into loops and
  then bands in the superstructure of chromosomes

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Chromosomes
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Chromosomes
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Chromosomes
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Chromosomes
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DNA and RNA

• The three differences in structure between DNA
  and RNA are
• DNA bases are A, G, C, and T the RNA bases are
  A, G, C, and U
• the sugar in DNA is 2-deoxy-D-ribose in RNA it
  is D-ribose
• DNA is always double stranded there are several
  kinds of RNA, all of which are single-stranded